The comet assay is a sensitive and rapid method for DNA strand break detection in individual cells. Its use has increased significantly in the past few years. This paper is a review of the studies published to date that have made use of the comet assay. The principles of strand break detection using both the alkaline and neutral versions of the technique are discussed, and a basic methodology with currently used variations is presented. Applications in different fields are reviewed and possible future directions of the technique are briefly explored.